Our laboratory has been primarily involved with biochemical studies of cultured ACTH-responsive mouse adrenal cortical tumor cells. Recently, we have been interested in correlating morphological data with biochemical effects of ACTH and other steroidogenic agents. We have completed a comprehensive electron-microscopic analysis of the tumor from which the cells are derived and unstimulated primary cultured cells after various intervals in vitro. We have also determined some ultrastructural effects of ACTH and cholera toxin on cells stimulated for 90 min to 2 h. The proposed research will extend our observations of acutely stimulated tumor cells to include investigations employing cinemicrography, SEM (scanning electron microscopy), stereoscopic HVEM (high voltage electron microscopy) and additional cTEM (conventional transmission electron microscopy). By these approaches, we will obtain information concerning the appearance of microfilaments and microtubules in these cells and associations of the cytoskeleton with other organelles implicated in steroid biosynthesis or secretion. We will determine the effects of ACTH or other stimulatory agents on this morphology and on the steroidogenic function of the cells. We will also determine the degree to which known inhibitors of the cytoskeletal elements mimic or inhibit these structural and functional changes. From our data, we will construct a model which will delineate the role of the cytoskeleton in the "rounding-up" of the acutely stimulated cells and the onset of increased steroid production. The effects of long-term (trophic) stimulation by ACTH on the cytoskeleton and on other organelles having known or suspected roles in steroid production will be investigated. These studies should provide a basis for similar investigations of hormone action in other cell systems.